Apply asm redirections in stdio.h before first use [BZ #27087]

Compilers may not be able to apply asm redirections to functions after
these functions are used for the first time, e.g. clang 13.
Fix [BZ #27087] by applying all long double-related asm redirections
before using functions in bits/stdio.h.
However, as these asm redirections depend on the declarations provided
by libio/bits/stdio2.h, this header was split in 2:

 - libio/bits/stdio2-decl.h contains all function declarations;
 - libio/bits/stdio2.h remains with the remaining contents, including
   redirections.

This also adds the access attribute to __vsnprintf_chk that was missing.

Tested with build-many-glibcs.py.

Reviewed-by: Paul E. Murphy <murphyp@linux.ibm.com>

1 files changed, 12 insertions, 5 deletions

diff --git a/libio/stdio.h b/libio/stdio.h
index e6425341ce..0e0f16b464 100644
--- a/libio/stdio.h
+++ b/libio/stdio.h
@@ -885,20 +885,27 @@ extern void funlockfile (FILE *__stream) __THROW;
 extern int __uflow (FILE *);
 extern int __overflow (FILE *, int);
 
+#if __USE_FORTIFY_LEVEL > 0 && defined __fortify_function
+/* Declare all functions from bits/stdio2-decl.h first.  */
+# include <bits/stdio2-decl.h>
+#endif
+
+/* The following headers provide asm redirections.  These redirections must
+   appear before the first usage of these functions, e.g. in bits/stdio.h.  */
+#if defined __LDBL_COMPAT || __LDOUBLE_REDIRECTS_TO_FLOAT128_ABI == 1
+# include <bits/stdio-ldbl.h>
+#endif
+
 /* If we are compiling with optimizing read this file.  It contains
    several optimizing inline functions and macros.  */
 #ifdef __USE_EXTERN_INLINES
 # include <bits/stdio.h>
 #endif
 #if __USE_FORTIFY_LEVEL > 0 && defined __fortify_function
+/* Now include the function definitions and redirects too.  */
 # include <bits/stdio2.h>
 #endif
 
-#include <bits/floatn.h>
-#if defined __LDBL_COMPAT || __LDOUBLE_REDIRECTS_TO_FLOAT128_ABI == 1
-# include <bits/stdio-ldbl.h>
-#endif
-
 __END_DECLS
 
 #endif /* <stdio.h> included.  */